Various devices attached to the body by a belt have been developed to aid in the exercising of the abdominal muscles. For example, U.S. Pat. No. 2,163,107 discloses a gravity based device having a heavy curved weight for positioning on the abdomen when the user is supine. A belt from one side of the weight around the back of the user to the other side retains the weight in place on the body. The abdominal muscles are exercised by alternately partially relaxing against the force of the heavy weight and then tightening to push the weigh up. U.S. Pat. No. 3,278,185 shows a device similar in method of use that substitutes a spring for the weight. One end of the belt is attached to one end of the spring and the other end of the belt is attached to the other end of the spring. The muscles are exercised by tightening against the resistance of the spring to press the device outward. U.S. Pat. No. 3,532,340 shows a different type of exerciser secured to the body by a belt. A hula hoop type of ring is spaced from the belt and is attached to it by a plurality of springs. The user exercises the abdominal muscles in a standing position by holding the ring steady with his hands and then rotating the lower body against the force of the springs using the abdominal muscles. U.S. Pat. No. 4,603,858 shows a lever and spring based abdominal exerciser. An axle is secured to the abdomen by a belt. A lower lever of the device rests against the fronts of the legs. An upper lever of the device is held by the hands and rotates about the axle toward the lower lever. A spring between the levers resists movement. The abdominal muscles are exercised when they are used to bend the body and the upper and lower levers toward each other against the resistance of the spring.
The latter two devices require movement of the body in addition to the tightening and relaxing of the abdominal muscles. Undesirable twisting, bending, or stress on the backbone and tailbone may result. Also, the movement of the body requires the use of other muscles resulting in more rapid fatigue than if the abdominal muscles are exercised alone.
In contrast, the first two devices allow the exercising to be focused on the abdominal muscles. The first device, however, never allows the muscles to be completely relaxed because of the heavy weight which continuously presses down and must be counteracted to avoid injury or discomfort. The second device has somewhat limited utility because of the requirement to maintain the belt tightly around the abdomen. The repeated relaxing and tightening of the abdominal muscles causes the device to pull and chafe the skin. A device that allows the exercise to be focused on the adbominal muscles without injury or discomfort to the skin or body during use would provide significant advantages.